Fin assembly for fin-stabilized projectiles, and a process for its manufacture

ABSTRACT

A fin assembly for use with fin-stabilized projectiles such as grenades and mortars includes a tail carrier tube with a plurality of longitudinally extending fins projecting radially from the tube, the base or foot portion of each fin being pressfitted into the material of the tail carrier tube. The fins are composed of a material having substantially greater strength than the material of the tail carrier tube, and the foot portion of each fin preferably has an undulated configuration with respect to the longidutinal axis of the fin.

United States Patent Donner et al.

[ Oct. 16, 1973 FIN ASSEMBLY FOR FIN-STABILIZED PROJECTILES, AND A PROCESS FOR ITS MANUFACTURE Inventors: Frederic Arno Donner, Helsinki;

Niilo Kalervo Asikainen, Tampere, both of Finland Assignee: 0y Tampella Ab, Tampere, Finland Filed: July 9, 1971 Appl. No.: 161,367

Foreign Application Priority Data July 11, 1970 Germany P 20 34 568.0

US. Cl. 3 24473.23, 10 2/4911 Int. Cl. .L F42b 13/22 Field of Search l02/49.1, 49.2;

References Cited UNITED STATES PATENTS 5/1962 Lyon 244/324 X 3,238,875 3/l966 Stadler et al 244/324 X FOREIGN PATENTS OR APPLICATIONS 1,032,036 3/1953 France 244/324 Primary ExaminerVerlin R, Pendegrass Attorney-Marva & Smith 11 Claims, 4 Drawing Figures FIN ASSEMBLY FOR FIN-STABILIZED PROJECTILES, AND A PROCESS FOR ITS MANUFACTURE This invention relates to a fin assembly for finstabilized projectiles such as grenades and mortars and to a process for manufacture of the same.

Fin-stabilized projectiles are generally designed with fin assemblies which are produced separately and then secured to the rear portion of the projectiles. Each fin assembly generally consists of a cylindrical carrier tube with a plurality of vanes extending radially from the circumference of the tube and longitudinally of its axis. The fin assembly is generally produced as a unitary one-piece construction by an extrusion process with a central carrier tube and seven to ten vanes distributed about the circumference of the tube. With this construction the vanes necessarily are shaped with a high degree of rounding as seen in cross-section, since the foot portion of each fin has an arcuate configuration which blends into the circumference of the carrier tube. This configuration results in a relatively wide forward frontal surface on each vane offering air flow resistance which unfavorably influences the range of the projectile. Also, the vanes along with the carrier tube are usually manufactured from a light alloy material, and thus the vanes are subject to deformation or damage when the projectile is fired.

It is an object of the present invention to produce a fin assembly for fin-stabilized projectiles which has a better aero-dynamic shape and withstands greater stress without being deformed.

It is a further object of the invention to produce a fin assembly for fin-stabilized projectiles which may be readily and cheaply assembled.

Briefly, the fin assembly of the present invention comprises a tail carrier tube and a plurality of longitudinally extending fins, the foot portions of which are press-fitted into the material of the tail carrier tube whereby they project radially from the tube. The fins are produced from a material having substantially greater strength than the material of the tail carrier tube, and preferably parts of the foot portion of each fin are offset transversely to the longitudianl axis of the fin for additional strength and for securing the foot portion in the material of the tail carrier tube.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which:

FIG. 1 is a side view of a fin for use in the fin assem- FIG. 2 is a front view of the tin shown in FIG. 1 as seen in the direction of arrow II;

FIG. 3 is a bottom view of the fin shown in FIGS. 1 and 2 as seen in the direction of the line III-III of FIG. 2; and

FIG. 4 is a side view partly in section of a fin assembly including a tail carrier tube with fins fitted thereon.

The fin shown generally at l in FIG. 1 is producedfrom a high strength material such as steel, e.g., chrome molybdenum steel. The fin 1 includes a leaf-shaped part 2 which is relatively thin, about 2 mm. thereby offering a small frontal surface and limited. air resistance. The forward portion or shoulder 3 of the fin is tapered to further reduce wind resistance and is at an acute angle. Behind the shoulder 3 is a generally fiat portion 4 having the greatest cross-section of the fin, and this is then tapered towards the rear at 5. The foot portion of the fin is shown generally at 6 and includes a seriesof undulations 7 and 8, the transitional part 9 between the undulations 7 and 8 having essentially the same crosssection as the undulations 7 and 8. The result is an undulating uninterrupted double surface defined by a straight line as viewed in FIG. 3.

Each of the fins is secured to the tail carrier tube of the projectile by pressing each fin into the tail carrier tube. The tail carrier tube consists of a softer material than that of the fins, thus permitting the foot portion of each fin to be pressed into the carrier tube. A preferred material for the carrier tube is an aluminum alloy comprising A l, Zn, Mg and Cu (1.5, F54). The alloy is preferably softened by heating it to a temperature of be- WEEHZSW and 350C before the fins are press-fitted into the carrier tube. Although a groove for receiving each tube is provided in the surface of the carrier tube if the fins are inserted while the carrier tube is cold, the grooves are not necessary if the carrier tube is heated prior to pressing in the foot portion of the fin.

The undulated configuration of the foot portion 6 of the fin provides considerable reinforcement of the foot portion when the fin is being press-fitted into the carrier tube. Furthermore, the undulations 7 and 8 being offset to the longitudinal axis of the fin prevent movement of the fin in an axial direction relative to the carrier tube. Thus, when the fins are press-fitted in the carrier tube, they are secured rigidly and permanently.

When a groove is provided in the surface of the carrier tube for each of the fins, the groove must be narrower than the thickness of the material forming the foot portion of the fin and should be shallower than the height of the foot portion. When grooves are provided, it is not necessary to heat and soften the material of the carrier tube.

A special tool designed specifically to retain the fin is used'to press each of the fins into the carrier tube. The foot portion of each fin is pressed into the surface of the carrier tube to a depth sufficient to completely embed the offset undulations 7,8 which would otherwise offer considerable wind resistance.

The fin assembly of the present invention offers a number of advantages over the prior art fin assembly designs. The fins can be maintained relatively thin even at the base of the fin, thus reducing air resistance which otherwise results when the fin is widened at its base where it joins the tail carrier tube. The fins are more rigidly mounted with respect to the carrier tube in view of the press fit of the foot portion of the fin in the relatively thick carrier tube wall. Manufacture of the fin assembly is simplified while obtaining these advantages.

Furthermore, since the fins are produced from a material of relatively high strength, they are not prone to deformation at the time the projectile is fired which was a common problem with a fin assembly produced by the extrusion method. Thus, the flight path of the projectile is rendered more accurate and reliable which is particularly important with projectiles designed for extremely high flight speeds.

It will, of course, be understood that various modifications may be made in the disclosed arrangement without departing from the scope of the invention.

We claim:

1. A fin assembly for fin-stabilized projectiles such as grenades and mortars comprising a. a tail carrier tube b. a plurality of longitudinally extending fins projecting radially from said tube and longitudinally of the tube axis,

c. each of said fins comprising a main portion and a foot portion, said foot portion extending along a longitudinal edge of said fin and being embedded in the material of said tail carrier tube,

d. said longitudinally extending foot portion of each fin comprising a plurality of adjacent sections projecting alternately in both lateral directions beyond the planes defined by the respective opposite surfaces of the main portion of the fin,

e. whereby said fins are permanently secured to said tail carrier tube and movement of said fins with respect to said tail carrier tube in both the longitudinal and radial directions is prevented.

2. A fin assembly according to claim 1 wherein the material of said fins is of substantially greater strength than the material of said tail carrier tube.

3. A fin assembly according to claim 1 wherein the foot portion of each fin has an undulated configuration with respect to the longitudinal axis of the fin.

4. A fin assembly according to claim 1, wherein the sections of said foot portion are joined by transitional portions extending transversely of the longitudinal axis of said tail carrier tube and fin between adjacent sections.

5. A fin assembly for fin-stabilized projectiles such as grenades and mortars comprising a. a tail carrier tube b. plurality of longitudinally extending fins projecting radially from said tube and longitudinally of the tube axis,

0. said fins being composed of steel and said tail carrier tube being composed of an aluminum alloy, and

d. each of said fins having a foot portion press-fitted into the material of said tail carrier tube.

6. A process for manufacturing a fin assembly for finstabilized projectiles such as grenades and mortars comprising a. providing a tail carrier tube composed of a relatively low strength material,

b. providing a plurality of elongated fins composed of a relatively high strength material, such fin including a foot portion adjacent an edge thereof, and

c. pressing the foot portion of each of said fins in a radial direction towards the axis of said tail carrier tube through the surface of said tail carrier tube to a sufficient extent such that the surface of the tail carrier tube and adjacent portion of the low strength material is deformed and the foot portion of each fin is embedded in the low strength material of said tail carrier tube.

7. A process according to claim 6 wherein said fins are composed of steel and said tail carrier tube is composed of an aluminum alloy and is heated to a temperature between 250 and 350C. before the foot portion of each fin is pressed into the surface of said tail carrier tube.

8. A process according to claim 6 wherein a plurality of elongated grooves are provided in spaced relationship in the surface of said tail carrier tube, each of said grooves being narrower than the cross sectional width of the foot portion of each of the fins, said pressing step causing the foot portion of each of said fins to be pressed into each of said grooves expanding and de forming said groove as said foot portion is embedded therein.

9. A process according to claim 8, wherein the depth of each of said grooves is shallower than the height of the foot portion of each of said fins such that during said pressing step the foot portion of each of said fins deforms the bottom of each of said grooves to completely embed said foot portion in the low strength material of said tail carrier tube.

10. A process according to claim 6, wherein said foot portion of each of said fins comprises a plurality of adjacent sections projecting alternately in both lateral di' rections beyond the planes defined by the respective opposite surfaces of the main portion of the fin such that upon pressing the foot portion into the material of said tail carrier tube movement of the fin with respect to the tail carrier tube in both the longitudinal and radial directions is prevented.

11. A process according to claim 10 wherein said adjacent sections of said foot portion are joined by transitional portions extending transversely of the longitudinal axis of said tail carrier tube and fin. 

1. A fin assembly for fin-stabilized projectiles such as grenades and mortars comprising a. a tail carrier tube b. a plurality of longitudinally extending fins projecting radially from said tube and longitudinally of the tube axis, c. each of said fins comprising a main portion and a foot portion, said foot portion extending along a longitudinal edge of said fin and being embedded in the material of said tail carrier tube, d. said longitudinally extending foot portion of each fin comprising a plurality of adjacent sections projecting alternately in both lateral directions beyond the planes defined by the respective opposite surfaces of the main portion of the fin, e. whereby said fins are permanently secured to said tail carrier tube and movement of said fins with respect to said tail carrier tube in both the longitudinal and radial directions is prevented.
 2. A fin assembly according to claim 1 wherein the material of said fins is of substantially greater strength than the material of said tail carrier tube.
 3. A fin assembly according to claim 1 wherein the foot portion of each fin has an undulated configuration with respect to the longitudinal axis of the fin.
 4. A fin assembly according to claim 1, wherein the sections of said foot portion are joined by transitional portions extending transversely of the longitudinal axis of said tail carrier tube and fin between adjacent sections.
 5. A fin assembly for fin-stabilized projectiles such as grenades and mortars comprising a. a tail carrier tube b. a plurality of longitudinally extending fins projecting radially from said tube and longitudinally of the tube axis, c. said fins being composed of steel and said tail carrier tube being composed of an aluminum alloy, and d. each of said fins having a foot portion press-fitted into the material of said tail carrier tube.
 6. A process for manufacturing a fin assembly for fin-stabilized projectiles such as grenades and mortars comprising a. providing a tail carrier tube composed of a relatively low strength material, b. providing a plurality of elongated fins composed of a relatively high strength material, each fin including a foot portion adjacent an edge thereof, and c. pressing the foot portion of each of said fins in a radial direction towards the axis of said tail carrier tube through the surface of said tail carrier tube to a sufficient extent such that the surface of the tail carrier tube and adjacent portion of the low strength material is deformed and the foot portion of each fin is embedded in the low strength material of said tail carrier tube.
 7. A process according to claim 6 wherein said fins are composed of steel and said tail carrier tube is composed of an aluminum alloy and is heated to a temperature between 250* and 350*C. before the foot portion of each fin is pressed into the surface of said tail carrier tube.
 8. A process according to claim 6 wherein a plurality of elongated grooves are provided in spaced relationship in the surface of said tail carrier tube, each of said grooves being narrower than the cross sectional width of the foot portion of each of the fins, said pressing step causing the foot portion of each of said fins to be pressed into each of said grooves expanding and deforming said groove as said foot portion is embedded therein.
 9. A process according to claim 8, wherein the depth of each of said grooves is shallower than the height of the foot portion of each of said fins such that during said pressing step the foot portion of each of said fins deforms the bottom of each of said grooves to completely embed said foot portion in the low strength material of said tail carrier tube.
 10. A process according to claim 6, wherein said foot portion of each of said fins comprises a plurality of adjacent sections projecting alternately in both lateral directions beyond the planes defined by the respective opposite surfaces of the main portion of the fin such that upon pressing the foot portion into the material of said tail carrier tube movement of the fin with respect to the tail carrier tube in both the longitudinal and radial directions is preVented.
 11. A process according to claim 10 wherein said adjacent sections of said foot portion are joined by transitional portions extending transversely of the longitudinal axis of said tail carrier tube and fin. 